These studies seek to assess the effects of environmental agents on spermatogenesis, male accessory glands, and male reproductive capacity. Mechanisms of toxicity are studied and new approaches to toxicity testing are proposed and validated in order to extrapolate more reliably from laboratory animals to man and to improve our ability to analyze risk. The following studies are on-going: (1) species differences in DNA repair capability have been identified and the underlying biological processes which account for such differences are being sought; (2) the biotransformation of polycyclic aromatic hydrocarbons by cell free testicular homogenates and microsomes are being compared qualitatively and quantitatively to results obtained with the isolated perfused testis preparation; (3) the mechanisms by which DNA-damaging alkylating agents increase the TCDD induction of aryl hydrocarbon hydroxylase activity in the prostate gland 5 fold are being investigated; (4) the effects of gestational exposure to TCDD on the testicular development and reproductive performance of male offspring are being described; and (5) quantitative radioautographic studies using computer assisted image enhancing is being used to further define the blood-testis barrier.